RewriteEngine On
RewriteBase /
RewriteRule ^index.php$ – [L]
RewriteRule ^newadmin/?$ /wp-login.php [QSA,L]
RewriteRule ^newadmin/register/?$ /wp-login.php?action=register [QSA,L]
RewriteRule ^newadmin/lostpassword/?$ /wp-login.php?action=lostpassword [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
In this case you have to change the rewrite rule and provide a location for the wordpress. Above there are default .htaccess entries. Try to change it on your own.
For Example:
RewriteEngine On
RewriteCond %{HTTP_HOST} ^(www.)?example.com$
RewriteRule ^(/)?$ my_subdir [L]
RewriteRule ^index.php$ – [L]
RewriteRule ^newadmin/?$ /wp-login.php [QSA,L]
RewriteRule ^newadmin/register/?$ /wp-login.php?action=register [QSA,L]
RewriteRule ^newadmin/lostpassword/?$ /wp-login.php?action=lostpassword [QSA,L]
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
I am not an expert, but you must try to change it on your own, to be able to set this properly. Or maybe owner of the plugin will be able to help.
I was using these sites:
https://codex.wordpress.org/Giving_WordPress_Its_Own_Directory
https://stackoverflow.com/questions/2322559/htaccess-wordpress-exclude-folder-from-rewriterule
https://codex.wordpress.org/Multisite_Network_Administration