By default, all your Linguists will have access to the Translation step of your workflow, and you can only assign them jobs in the Translation step. If one of your Linguists should also be able to access the Editing (or other) workflow steps, you can change their permissions accordingly as described below.
You will see the list of all Users. Please note that the list will include Linguists and Project Managers of all languages.
Click on the "Filter" button in the top right corner, and enter the name, email or language of the Linguist that you are looking for into the corresponding fields. Click "OK" to apply the filter.
When you see the details of the Linguist, click on "Edit" in the top right corner.
Scroll down to the "Relevancy" section of the Linguist details, click on it to open it, and scroll down again to select the workflow step(s) that the Linguist should have access to. Click "Save".