Migrating from utf8mb4 to utf8 – bad encoding and

Hello
I transfered archidiecezjalubelska.pl site from company server (with MySQL 5.5.9) to older server (with MySQL 5.1.73-1). Offcourse there was no utf8mb4 encoding there so after exporting .sql file i opened it with notepad++ and did “replace all” function for utf8mb4 to utf8. Site is running however encoding on it is broken and i cant get to wp-admin site (its blank).

I tried export the base second time with MYSQL40 compatibility and import it with it but it was even worse (there were no colors set on the theme, some things were reset, and offcourse encoding problem with blank wp-admin site was still there. For blank wp-admin i tried to change plugins and/or themes directories for empty ones to be sure that its not something connected with particular plugin or theme. Nope, doesnt helped.

Ive read about DB Migrate plugin so far i dont have wordpress access to original database (changed DNSes) and can only log there by phpmyadmin. Changing back DNSes to original server and trying plugin without assurance that it work is not what i would try in first place.

So what can be done to repair those encodings?