How many times can I submit my app to iTunes Connect?
I'm not aware of any documented maximum number of times you can submit an app for review (source: App Store Review Guidelines).

The Review team will take the most-recent review request and start their review process, based on my experience over a few years.  When you submit a new version for review, the previous version is no longer eligible for review.

The only time you need to be concerned is when the review has already started (you've been notified that it's started) and then you want to do an update.  To avoid this situation, just be sure you really want them to do the review and your app is ready before you tap the 'submit' button.