If you give me a list of what you currently have, and explain the end result you want to accomplish, I can tell you how to get there. For example, list web apps, regions, resource groups, app service plans, SKU for each. If you moved something to a different resource group after it was created that is important since the original resource group is what matters.
It might help if you detail the reason why you want to make the change(s). For example, you are trying to consolidate the total number of app service plans you have, or perhaps you are trying to switch to a specific Premium SKU and it isn't giving you the option.
Bottom line there are cases where you need to re-create an app so that you can have it in a different app service plan (and underlying webspace) than it is in now.
NOTE: Feel free to obfuscate names of regions/resource groups/apps/etc. if that is your preference. Main thing is to be consistent.