PowerApps Forms Opening as Modal Popups on SharePoint List Instead of Side Panel
Hello rahulbarua
As of the moment, there is currently no quick way for this.
The one solution I can think of is creating a custom CSS and javascript for the site and deploy it using SPFX (SharePoint Framework). That will be a whole lot to learn.
Another course of action is to backup your current app and resize the current one to fit the new modal size.
Regards,
Charven