Hi
Issue is resolved,
I Tried switching to the default theme automatically by renaming current theme’s folder inside wp-content/themes and adding “-old” to the end of the folder name using File manager. That get my site back up and back into the admin area.
Next, I downloaded a fresh copy of my theme, uploaded it folder to wp-content/themes and then extracted it over there and Finally, tried switching back to (now updated) theme.
credits: esmi