This assumes that there is an existing template already created. If not, then create a new template first.
Click Dashboard
Click the Module e.g. Click Speaker module for the Submission Module
Click Settings button to open the Module Settings screen
For the Module Template field, select the template to be used
Scroll down, click Update button to apply changes
Changing the template used in the Forms Module
In the forms module each defined form uses a template, it will typically use the default template or the associated conference template unless a specific template has been configured when your form was created.
Click Dashboard
Click Forms
Click on the Form name
Click Settings in the left side menu
Select Manage Settings
In the Form Template field, click the dropdown and select the template to use