How do I auto fill the form after selecting an option?

Unfortunately, that is not possible with Airtable's native forms, but you can do that with Fillout’s advanced forms for Airtable.

Fillout is 100% free and offers hundreds of features that Airtable’s native forms don’t offer, including the ability to update Airtable records with a form, display Airtable lookup fields & Airtable rollup fields & Airtable attachments & formulas on forms, dynamically & conditionally filter linked record fields by any values that you would like, perform math or other live calculations on your forms, accept payments on forms, create multi-page forms with conditional paths, create new linked records on a form, display as many fields as you want to see in a linked record selection list (including attachments), connect a single form to dozens of external apps simultaneously, limit the number of linked records that can be chosen, set advanced field validations & limitations, upload an unlimited amount of attachments simultaneously, add CAPTCHAs to your form, add choice matrixes to your forms, direct integration with hundreds of apps like Calendly & Google Maps on your forms, and so much more. 

Hope this helps! If you’d like to hire an expert Airtable consultant to help you with anything Airtable-related, please feel free to contact me through my website: Airtable consultant — ScottWorld

Airtable does not currently have dependent dropdown values in forms, however, there are some potential workarounds to your workflow.
- If the form submitter does not really need to see this ID and you're only interested in linking it to the record submission on the backend for base editors, you can set up an automation to do this based on Windows Login Id when the form is submitted.
- You can also pre-populate fields on a form using URL query parameters and set up an automated way to send custom form links to the correct submitter. More info on pre-filling forms https://support.airtable.com/docs/prefilling-a-form

Thank you for the reply!  Unfortunately, pre-filling form is simply not possible as the form is mainly for the asset managing personnel to use to quickly update details. We would need to search through the user list to find the specific URL before using the form, which would beat the purpose of the form itself.

ID is still required but I haven't really thought of using automation fill in the other parts. Perhaps I will try that method.

Thank you for the reply! Seems like using an Integration is the only way to go if I want to design the form in that way. It's a pity that Airtable's form is not able to do so, hopefully they would a feature like this in the near future.

Hey there, I just wanted to add that our miniExtensions Form can be a great fit for use cases like this one! It offers a login functionality for example, where you could look up a record associated with a certain ID and show everything related to it. It's very straightforward to set up and you can try it out with a free account today! 🙂