Keyboard and trackpad not working properly after water spillage

Unfortunately, I spilled water on my MacBook Air 11"s keyboard and trackpad. It happened 5 days ago, and I took all the necessary measures right after it happened (turning it upside down, drying it, leaving it turned off for at least 48 hours in an upside down position.) After 2 days, I visited an Apple authorised service where they opened it up to see if there was any water damage (corrosion etc.) and they reassured me that there wasn't.

However, the keyboard and the trackpad stopped working properly from time to time. It often happens when I am using the upper second row of the keyboard; the keyboard stops working partially or completely while the trackpad does not allow me to left-click. I visited the same service regarding the issue but they told me that they would need to take the computer in for at least 5 days, and I sincerely can't trust their judgement anymore.

What can I do to determine what and where the problem is?

Thank you all in advance.