Prepend phrase + bruteforce

Hi everyone!

I'm trying to brute force a longer password of an unknown length. I probably know how the password starts, but then I need to brute force an additional 7-10 more charcters.

Is there a mode or way to prepend my guess / what I have in front of the brute forcing?

I didn't seem to find what I was looking for after reading through attack modes and the docs. I probably missed it or didn't understand.

Thanks for your help and patience!