just change fluid/filter and continue to drive

aged fluid creates friction during gear change. the symtom could be gone afterward.

at the worst, drive it until undrivable then rebuild your tranny for less than 1 grand, which will make you another 200kmi.

suggesting don't go to dealers unless for recalls or buying rare parts.  go to a reputed tranny shop for tranny service or a good mechanic shop for general services.