Hi there! While we don't currently have the option to automatically add leading zeros to a number field, you can still implement leading zeros in your app.
This will have to be created using a short text field with Conditional Rules. Let's call this field Zeros. The Zeros field will have 4 conditional rules, if you want numbers with 5 digits. The rules will be as follows:
1. If AI (your auto-increment field) is less than 10, set value to 0000
2. If AI is less than 100 and greater than 10, set value to 000
3. If AI is less than 1,000 and greater than 100, set value to 00
4. If AI is less than 10,000 and greater than 1,000, set value to 0
Then add a text formula that combines the Zeros field with the AI field for an auto-increment with leading zeros. You can also add whatever pre/post text you desire to that text formula.