For this you just have to qualify for FUT Champions, you don't have to participate.
Generally it takes 1250 points to qualify for FUT Champions, but afaik number can be slightly different.
You get points after matches in FUT Rivals and amount of points depends on the match result and your rank in Rivals. And also your current points display after every match so you can keep track of them.
For example on Rank 6 you will get:
Numbers are approximate (because I don't remember them exactly).
Every rank amount of points you're getting increases, so it is recommended to try get a win.
It's very easy to qualify currently, because end of season is scheduled in almost a year from now.
After you get needed amount of points achievement will pop.