There are several settings such as this that cannot be changed after they are deployed. Primarily, this is because the data is stored differently in the database (different field type or different tables etc). 

What to do? If this is a brand new process app that does not have any live data, you can undeploy the process app. This will delete all the related tables and the data in those tables. (This is why you should only undeploy if the process app is new. All the data will be deleted.) Once the process app is deleted, you will be able to make changes more freely (until the next deploy).

If this is not a new process app, you will need to delete the fields in Composer, and make new fields with the right settings.

Thanks Vickie Ortega  , how to undeploy the application? and is there a way to delete the table from the process app so that I can add a new table? and its better to delete the tab;e from the SQL database as well.

I would never recommend updating the database directly unless someone from the support team or the development team told you do this. Absolutely DO NOT delete a table directly from the database.

Are you sure there is no data in this process app that you need to keep? Undeploy will delete all of the data in the process app, and there is no way to recover from this (other than restoring the database to a previous backup). Everything in the primary table and all of the Aux tables that are defined in this process app will be deleted. It is much safer to delete the fields that we created with the wrong settings and create new fields with the correct settings.

its a new application that I am building from scratch and didn't go to PROD yet, so yeah I undeployed it and working on adding the right fields and other elements. I am cautious about undeploying or deleting anything of any PROD application

Thank you Vickie Ortega