Here are three things that many have found helpful starting work after the summer and summer holidays.
Book "startup time" in your calendar
I suggest 2 half days per week, for the next 3 weeks. Just block it now, so you have 2 half days protected every week. (Don't worry it will fill up…!)
This is your buffer time. It's time you can spend to catch up on things you did not complete before vacation. Time to deal with unexpected situations that may show up in the next few weeks. Time to clean up lists and mails or any backlog, and so on.
Extend your feeling of vacation
Leave work early. (Not too early, though!)
Make sure you extend the value of having had a vacation by making sure you leave work on time and take the evenings entirely off for some time now.
Leave work at work and be free in your free time.
No catching up on that mail from June you found in a folder. No spending hours in the evening to plan ahead. No spending time outside work-hours to plan and prepare or clean up old stuff. Do that during your workday. Then just go home regardless of how much is still undone. People you work with, customers and suppliers are often more understanding this time of year. Everyone else is getting back from vacation too!
Put yourself first
Just decide to make yourself your first priority for the next few weeks (should really be forever but we'll get back to that in some of those coming videos)
Your time. Your Energy, Your wellbeing. - You being present, focused, and inspired is more important than anything.