Can I limit free shipping to USPS First Class?

[tfc2020]

Hello! This is my first-time offering free shipping and want to limit it to USPS First-Class shipping, if possible. I've combed through different settings to see if I can find an option to do this. Is it possible? 

[AshleyK]

Hi! Thanks for reaching out and welcome to the Seller Community. Are you using RTS or just making your own shipping rates? If you add a rate called “free shipping” you can use whatever USPS service you want for it.

I would check your USPS settings to see if what options you have there.