how to replace 20% to - or underscore in theard url?

[Qleb]

Hi

im looking to remove the 20% ( spaces ) from the Theard URL and replace it with hypen or underscore

example :

https://vborg.vbsupport.ru/how%20i20%remove%20this.html

i need it like

https://vborg.vbsupport.ru/how-i-remove-this.html

i try to use

PHP Code:

$what_here = str_replace( ' ', '_', $what_here); 


and i dono where to use it

ill donate the developer how give me hand with this

so please guys if thier is any way to do that ill pay for it