Mariadb innodb_buffer_pool_size

Dears,

We have an Centos 8 with 120gb 4 RAM
Mariadb database

We added approximately 250 devices and it work good. But with every new device started to appear DB and web service error.
By restarting mariadb and ngnix services the problem is resolving for 5-6 hours.
We added more 50Gb for storage
image
And for now we have 56GB free but as soon as we add new device the issue is back. We thought that DB didn’t ‘see’ added 50GB.
We found out that it is necessary to increase innodb_buffer_pool_size, but we have no idea where we must to add it.

For now is:
innodb_buffer_pool_size - 134217728
We want to increase it to 2gb

This is database question mostly.
I recommend to use this.

There are a lot of tutorials online that explains how to tune/configure mysql.