Yoast plugin Balise title

Hello,

I wanted to have a balise title that I choose instead of google choosing for me.
So I install YOAST SEO.

I follow all the instruction, however on my home page I can’t go further since my template doesn’t offer a text area. The pages are building yet.
It is hard to explain… but I just can’t follow all the insctructions of yoast since my template doesn’t offer me all the options to change the content.

Does someone can help me please?
Or let me know what other plugin can permit me to change my balise title?
It is very very important as you can imagine and I am totally lost with it.

Thank you very much in advance!
Regards