Bosch GCM10S compound mitre saw bevel lock stuck

Desperately hoping someone can help. I bought my first compound mitre saw recently..a secondhand Bosch GCM10S and just discovered that the bevel lock doesn’t budge. Funny, the guy selling it pointed at it but avoided showing me that it works. The manual just says “ release bevel lock”. Any ideas appreciated. Thanks, Karen

Is this the saw?

Yes that is the saw. I sprayed a bit of WD40 into the mechanism and after a few hours it was unstuck and the lever works with ease. I thought there might be a knack I didn’t know about but there isn’t. Thank you for replying!