I suggest taking a look at Adventures In FileMaking #2 - Enhanced Value Selection. This is a free to download FileMaker file with numerous fully functional examples of ways to select values from a list when a simple value list just won't cut it. Each example has very complete documentation and explanations on how it works and how it was set up. One of the examples allows the user to enter a Name but then the corresponding ID is looked up and used to link the two records. your tag's asset number could be that name, with the _equipmentID_fk value the "looked up" value.
There are also some auto-filtering search portal examples that work pretty well on iOS devices that may also be worth a look.
And here's one more idea: If you printed a barcode on those asset tags, iPhone users would not have to enter anything, you can set up a solution that scans the barcode and uses that value to look up date, create and link records or whatever is needed. (I use that method in two of my solutions--one of which tracks a special item of computer equipment that needs frequent replacement here where I am currently employed.)
Thanks, this is very helpful.