On the study toolbar there is the 'Edit Help button
You can edit the help text shown to users by clicking the pen icon. Any help text you enter here you quickly preview how the users would see it by selecting the 'Preview Help' button.
The export and import help buttons are predominantly used to transfer help from the UAT system to the Live system as many users like to setup help before going live. There is no reason to enter help on the UAT site once the study is on the Live site. Once you are happy with the help you can click the 'Export help' on the UAT site which will download a json file. On the Live system click 'Choose file' and select the help file and then click 'Import help'.