Synology installation trouble

Hello Guys.

I have a big problem. i tried to install nextcloud on my synology ds218se. (i install phpmy admin, mariadb 5 and 10) but i have a big trouble to the step 1 (Dependencies not found.
Can’t write to the current directory. Please fix this by giving the webserver user write access to the directory.). How can i fix thi problem?

Thanks in advance