Hi @Theresa400 , and welcome to Airbnb!
HST is NOT collected by the platform. If you are in a position where you MUST collect it (ie: expect more than $30k of revenue from your business in a year) then your options are:
1) Include hst in your nightly price by bumping it up 13% (obviously, mention that fact in your listing), and make the remittances yourself each quarter (which is likely not the preferred way), or:
2) Under your listing, there is a "local taxes and laws" tab. Under this you can add a tax, which will then be listed as a separate line item when a guest books. Here's the help article on that:
https://www.airbnb.ca/help/article/2523/how-do-i-add-taxes-to-my-listings
There are some caveats included in the help article, and you would still need to remit the funds yourself, but presumably the accounting is set up for you in transactions.
Do you have an hst account and registration number already? Have you checked with a professional CPA to make sure you need to collect hst?