wplms does not modify any behavior of woo-commerce.
We just use woocommerce recommended hooks.
You can check this doc: https://docs.woocommerce.com/document/checkout-field-editor/
If you want to show pincode and other fields here then we have an option for that.
please goto wplms -> miscellaneous ->enable remove extra checkout fields .
refer : http://prntscr.com/8yg5nz
Set it to No and save changes
The extra fields will start showing on the page. But for other fields, please follow the doc
Checkout page – User is logged-In in app but while checkout it again asking for login or need to create new account.
Suggestion: Already logged-in user details should be fetched while checkout so no need to ask user same information again.</p>