While inside your Squad that you're admin of, tap on the hamburger menu at the top left of the screen.
Tap on 'Squad Details' on the page that pops up.
Tap on 'Manage Squad Billing Plan', note that you have to be an admin in your Squad to change the billing plan.
On this page, you will see the 3 different plans for SquadPod, and the ability to pay monthly or annually based on your selection at the top of the page. Once you decide on the plan you want, tap on 'Update to this plan' and go through the billing prompts for the Google Play Store.
Finally, decide between a monthly or yearly subscription and scroll to view the different plans, and tap on 'Subscribe' once you've decided. You will then follow the prompts for the app store billing page to pay.