@Rachael-V0
Long term stays can be great for Hosts, but they can also turn into a real nightmare on Airbnb. Be sure not to get talked into more than a 20% discount (there is a common scam related to this). As @Marie8425 says, you'll only get paid one month at a time (not the full amount of the stay) and there are alot of pitfalls to be avoided. I'll post a link to a Monthly Stay Guide that might be helpful. I would take a look at that before committing to a 3month stay.
Host Guide to Monthly Stays
https://community.withairbnb.com/t5/Community-Guides/Monthly-Stays-on-Airbnb-Guide-Revised/td-p/2031...
That said, Hosts can do a special offer for monthly stays. Basically the guest sends you an inquiry or request to book. You then send them the special offer that includes the entire amount of the stay plus any cleaning fees (other fees). Airbnb will add their service and any taxes (if they apply):
Sending Special Offers
https://www.airbnb.com/help/article/35