Hello, Jennifer!
Is it possible? It sure is possible, but it's not very easy. In order to filter a lookup field, you'll need to send a request to the source list using JavaScript, get the items from this list that match your criteria and finally populate lookup field choice with the matching items.
It's doable, but Cross-site Lookup already includes this functionality, so there is no need to do everything manually. With just a few changes to the Advanced section of Cross-site Lookup you can get the same result, but much quicker. Here's an article on Cross-site Lookup filtering -
https://spform.com/cross-site-lookup/fi ... ite-lookup
If you'll have any additional questions, please, let us know!
P.S. If you want us to write the necessary code for you, send us a detailed request to the
support@spform.com Depending on the difficulty of the request, we'll estimate how much time it will take us to do and you'll be able to purchase extra support minutes, so we'll do all the manual work and troubleshooting for you.