Regrossissons - do t understand how I’m supposed to know about the prefix

Yes, prefixing a verb with re- changes its meaning to doing the action again:

partir -- repartir (to leave again)
faire -- refaire (to do again)
voir -- revoir (to watch again)
...

Actually, in English this works just the same:

to do -- to redo
to make -- to remake
to match -- to rematch

...

I thought I clicked that one but I think my finger hit the wrong button. I already know this rule it’s with the other pronouns like ils vs nous that I struggle with 

Oops I already know this one I hit the wrong button oops