Hello,
Please post different questions via separate topics.
1/ Edit the header > Header overlap > enable overlap on mobile – https://prnt.sc/TWEE3009RHpY
2/ There is only desktop and mobile view, the tablet inherit settings from mobile for the header. You can change Mobile Header Starts From value via Theme Options > General.
3/ Provide FTP access, please. If you do not know how to create FTP contact with your hosting provider, they will help you.
4/ Please describe the desired result in more detail.
Regards