Hashtopussy Mask Attack
How to use mask attack when using hashtopussy?
The problem is that this is not the hashtopussy forum.

Hashtopussy is a 3rd party software. You are asking your question at the wrong place
You should try to find the answers to your questions by reading the documentation of the 3rd party program that you use (in this case for instance this: https://github.com/s3inlc/hashtopussy/wiki)
You do it the same way as you would in hashcat. In the new task parameters, add -a 3 and then your mask.