Modification position into a hook

[Victoria123456]

Hello, 

Prestashop version : 1.7.7.1

I would like to modify the order of the module into a hook. To do so I try to do : Design > Positions > drag and drop the module at the position that I want. But Prestashop doesn't save the modifications. The order stay the same and the number in the list stay the same. 
On several previous topics I was that there should be small arrows to change the position but on my side I cannot find those arrows... 

Do you know how would it be possible to modify the order of the modules into a hook? 

Thank you in advance. 

Have a nice day,