The man at the service centre is correct, do not use an air can.
1) it probably won't get to the contact
2) it will blow any dust inside the keyboard around, with the potential (albeit slight) to cause other issues.
The correct procedure is to open up, access the contact(s) that are troublesome and gently clean it/them out with a cotton bud dipped in denatured alcohol. This type of contact has been in use by all makers since the 1980s, and it's been an issue since then for all of them. Some keyboards/pianos/synths/organs never have a problem, some will have lots. Depends to some extent on the use they keyboard gets and the environment it's in.
And never, ever follow the sometimes-given 'advice' to press the keys repeatedly, to press them hard or to 'wiggle' them. That worked for old style 'whisker' contacts but on rubber/carbon contacts, all it does is press the dust/dirt harder into the contact.