To answer your question, Yes. You can focus on boosting your metabolism since you can't freely do sport.
To answer the person that downvoted my answer, we can see that boosting one's metabolism is a commonly used concept in approved Health SE sources. E.g. based on this article on WebMD:
Can you change your metabolism? Yes. Whether you're born with a fast,
average, or slow metabolism, there are things you can do to speed
yours up or slow it down.
Source: Boosting Your Metabolism - https://www.webmd.com/diet/tc/boosting-your-metabolism-topic-overview
Here are some suggestions which I've put in application in my own life. Hope it helps somebody out there.
The idea is to extend as much as possible the fasting period around your sleep. E.g. to give myself as an example, I eat two times per day, once at noon and once at 6PM, fulfilling complete meals.
Some research shows that intermittent fasting works. In one study,
overweight adults who cut calories by 20% every other day dropped 8%
of their body weight within 8 weeks. They also had less inflammation.
Drink green tea/coffee throughout the day
In a small study, green tea appeared to raise metabolic rates and
speed up fat oxidation.
Improve the look of your abs with the vacuum exercise rather than crunches:
Helps strengthen the core and definitely improves the aesthetics of the abs.
Some other readings: