Pin Keep Reminder to notification shade?
There's no native way in Android to do it unless the app itself implements it. However, some hacky ways to achieve it-


Using apps - Boomerang Notifications and Pin Notifications
Using Tasker - https://www.reddit.com/r/tasker/comments/4orcfg/make_notification_persistent/d5h8ln9/
Xposed Module - https://forum.xda-developers.com/xposed/modules/4-1-pinnotif-pin-notifications-to-avoid-t2765095 (Not updated in a while, will be incompatible with latest versions of Android)