I assume you’re talking about the top left logo in the header, and that you find it too small.
Because you have additional buttons in your header, your logo will remain small. The best solution would be having an alternative logo more suitable, designed especially for small spaces, that could fit in a square.
After having made such a logo, you can upload it in https://forum.ubtask.com/admin/site_settings/category/branding
Look for mobile_logo.
Alternatives solution: hide or reduce the font size of your custom header’s button with CSS.