I’m not sure how I missed this post, my apologies.
This can not be done I’m afraid, Index is not a searchable field and there is also no “jump to index” button
On iOS you should have a “jump to” scrollbar which at least can get you in the middle of the list or end, quickly.
On Android when you start scrolling, a scrollbar should appear on the right hand side which you can “quickly grab” and “quick scroll” to get to an area quickly.
You can also sort Index asc. or desc. depending on your need today.
I use index number to store the bar code for my comics. So that I may search on the index number, put the index number into a JSON object in the Personal/Notes field. That being said, I do wish that the index number could be searchable. We scan the bar code on our comics to jump to the record for that book.
Example (Personal→Notes) (we also add other extra fields into this JSON object):
With the example above the sku can be searched by jut entering the sku or “sku”:”20422359”
You can modify the notes fields in bulk by creating a backup and then carefully editing the XML file and restoring. If you do this and are using the mobile app with syncing, you will need to remove the data on your mobile device (reinstall the mobile app clean) and then resync AFTER restoring; otherwise the mobile data will overwrite your edited data.