Welcome.
So you have a database form? Set up to query and submit to your access table?
You should be able to populate multiple query fields before you initiate the query and they will be used in the query. You can have your dropdowns have rules to set the query fields with their values then have a button or on the second drop down initiate the query.
First I would just put your query fields and data fields on a form and play with entering multiple fields for your query. Once this is working, then try adding seperate fields with dropdowns and use them to populate the query fields. Step by step is how you learn.
Good luck.