how to restrict "open a new case" in powerapps customer self service portal ?

Scenario : In the 1st picture in portal i have to write a code using liquid or javascript code in which only admin has a open a new case access and other users do not have a open a new case when other users are logged in it should show them that they cannot create any case how this can be achieved using powerapps ?

I have used liquid script hereby attaching the code , i created the web roles and new web template in new web template i have written the code 

{% if user.roles contains 'Administrators' %}
    {% open a new case: 'Entity Form with Button' %}
{% else %}
    {% open a new case: 'Entity Form without  Button' %}
{% endif %}

After creating web roles and creating web templates what steps do i need to follow , can anyone help resolve my query ?

Thanks & Regards,

Ainee Ahsan