I'm not sure if you can do this. As far as I am aware, you can hide the messages that you dont want to see. Usually swiping the messages to the right will hide them or holding you finger down on them is another way. I would try this to see if that works for your case. Maybe @Hotrod knows of a way that might be beneficial to you.
Keawe29 you cancel the trial by going to your active subscriptions.
Manage your Promote Plus subscription If you need to cancel your Promote Plus subscription, go to the link for your app store: * Apple * Android Your Promote Plus benefits will continue until the end of your current billing period. Then your monthly payments will stop, and if you have a Promote Plus promotion running, it will end. You can still re-subscribe at any time, or buy individual, limited-time promotions for any items you’re selling.
Keawe29 From your OfferUp app-> “My Account” Page-> scroll down tap “help”-> search “About Promote Plus” -> scroll down to “Manage your Promote Plus subscription”
Tap on iPhone or Android following instructions how to cancel.