In the free BIMx App you can purchase the BIMx PRO functionality with the "BIMx PRO license" option. This license can be used on four other devices (having the same Apple ID) by restoring the purchase. If the App was deleted from the device accidentally the previously purchased license can also be restored in BIMx the same way.
To restore your purchase follow these steps:
Connect to the App Store from BIMx
Highlight a 2D content from your project, then press the far right side of the highlighted row (you need to press the star with a lock on its top left corner). Choose Purchase option from the pop-up window.
Choose the Restore Purchase option
Three options appear, scroll down to the last one and choose the "Restore Purchase" option.
Sign in with your Apple ID
Sign in with the Apple ID you used for the original purchase. After this your purchase will be restored.