You are trying to modify a MS template db. It is using macro and TempVars for the search functionality.
The search works as designed. Form returns all records that match ID_Asset - there are 9. If you want to use multiple criteria then set up more TempVars and modify macro. Macros are intended for use by non-programmers. I don't use macros because they are harder to debug. I recommend converting macros to VBA.
Modifying db is a significant task and you either need to learn programming (macros or VBA or both) or pay a developer to build db. Extensive tutoring is beyond scope of forum venue.