Click Users in the sidebar menu, then click Capabilities.
In right sidebar type any role name (e.g. Pluginmanager) in Create New Role box and click Create button.
Select created Role and click Load button.
Select the following rights for the new role: activate plugins, read, update plugins, delete plugins, edit plugins, manage options, install plugins. Then click Save Changes.
Step 3. Add new plugin manager user.
Click Users in the sidebar menu, then click Add New.
Fill the form as shown in the screenshot. Select Pluginmanager from the list of roles and click Add New User button.