Welcome back! It's great to hear that you'd like to continue using your Pro features to help you reach your goals.
If you just canceled your Pro subscription, you'll still have access to those features until the end of your billing period. You'll have to wait until that passes and your account is switched back to a free account before you can go Pro again. Once your Pro plan completely expires, you'll be able to go to about.me/upgrade to reinstate your Pro subscription.
If you canceled your Pro subscription a while ago and your page already looks like a free page, simply go to about.me/upgrade to go Pro!