Football Manager 2021 Xbox Edition

Achievement objective:
Winning the "The Saviour Cometh" challenge

Challenge description:
Picking any team from any league - no matter how strong they are, the game starts off in the relegation area with a terrible start into the season. It is up to you - as a newly signed manager - to avoid relegation at all cost.

Achievement solution:
Here is what worked for me. A step by step guide:

1) Before starting off the challenge, set the difficulty to EASY.
2) You can pick any team from any league. I went for GERMANY and picked the 1.BUNDESLIGA team FC BAYERN MUNICH.
3) Start off the challenge, you will start off at rank 17.
4) In my case the game saved automatically in a regular manner. If I ever lost a match, I always returned to the main menu by hitting and moving the cursor the RETURN TO MAIN MENU. Reloading my game, it would always continue from the previously lost matchday. I'd only continue once I won the match.
5) Proceed forward by hitting the button through management decisions and status reports. Sometimes, you'll have to extend contracts or decide if a player should be transferred or not.
6) Once you enter the matchday tactics screen, move the cursor to QUICK-PICK (right above the SUBS tab). This way injured and booked players will be benched automatically, saving time. Afterwards, do not hit the -button. Instead, choose the option that's left from that tab. This way you can give instructions to your team and co-trainer, taking care of everything (basically, simulation).
Hint: Depending on the opponent and given status reports, pick your tactics accordingly.
Example given: If the opponent scouting report states that you'll probably get a greater victory against a team on a relegation spot, there is no reason to aim for a draw.
7) Proceed this way until the challenge is over. If the challenge has been won, the game will show a winning screen, offering the option to continue the season or return to the main menu. I highly suggest that you finish the season entirely and wait for the final board evaluations etc. This will net you a couple extra achievements for sure (Player of the Year awards, board satisfaction etc.).

Final words:
I didn't lose a single match following this method. However, I had to replay a single match about 4 times, as I had some key players missing. So I simply repeated step 4, which is what I'd recommend. Nevertheless, FC Bayern has a top tier squad and will easily dominate the 1.BUNDESLIGA. Starting off at rank 17, I finished the season at rank 6. It is impossible for a team like that to be relegated.
In the following I also unlocked the following achievements:

A pretty easy one to do.

Pick any big club, play on easy and save before every game. The first results may need a few reloads, but after a few positive results, it is easier as they pick up the form. I used Manchester United in the English Premier Division.

Edit: As some people are confused about what to do here, despite the achievement description and the game telling you what to do, I've updated and gave some more info below.

This is a challenge. As with all challenges, they are accessible from the main menu under the new game option. After selecting challenge mode, the very first challenge is called The Saviour Cometh. Underneath the name is the description of what you need to do: "your team are embroiled in a relegation battle halfway through the season. Can you take the reigns and guide them to safety?"

I hope that helps, but if you need further tips, feel free to comment below and I'll try to assist by updating the guide.

All you have to do is survive relegation whilst playing this challenge.