Hello there @tanmoyweb
I imported your form in a testing site of mine using no other plugin and the default TwnetyTwenty theme and the submit button wasn’t disabled at any point. This means that another plugin or theme is messing with that in your site, so a conflict test should be made around that in order to narrow it down.
How to:
First, create a recent backup in case you lose any settings during the test and have to restore to a previous working state.
Then deactivate all plugins apart from Forminator, activate a default theme like TwentyTwenty, clear all caches and check again if the issue is still there. If not, it means that something is conflicting, so start activating the remaining plugins and theme, one by one this time, checking every time for the reported issue, until you reproduce the issue, thus finding the conflicted combination. The following flowchart image can assist you during this test: https://premium.wpmudev.org/wp-content/uploads/2015/09/Support-Process-Support-Process.gif
If this is a live website with traffic, I’d rather advise to create a staging environment, meaning a complete and exact copy of this installation into another location/folder in the same server, using a separate database, and perform the test in there instead without worrying about the live site.
Looking forward to your results!
Take care,
Dimitris