I will take a different direction with my answer: "You cannot fix what you do not know!"
The first thing you need to do is to understand why the attendance is low / decreasing. You can find that out in at least 2 ways:
Make small changes in whatever you do, one at a time, see what it works. It will be slow and does not guarantee a satisfactory result.
Get actual information. Ideally, the students will tell you themselves what is going on - especially if you have a good relationship with them. Just ask them. Even better: do not ask about attendance, ask about feedback: about you personally and about the way you do your job. You may be surprised by the things you will find out.
Why feedback about you personally, you may ask? Well, we had a situation at a previous job. One guy (nice guy otherwise), was always emanating a smell of food, especially onions. One day, two days... For the colleagues near him, it was a nightmare to survive throughout the day. So one of them decided to suggest him (in private) to eat onions only in the evening. The answer was astonishing: he did not eat onions. The discussion revealed the true "monster": he was using deodorant with the smell of onions. What I want to say: the real reasons for things are not always obvious in any way. No other implication intended.
So you should not rule out reasons like color of shirt, haircut or God knows what else.
Bottom line: We can brainstorm about many things here. It is only you who can find out what is going on - and you may share the results with us. If you are more specific with details of the situation, we can be more specific helping you.