After the package has been installed, you need to establish a connection between Salesforce and sevDesk. To connect it, you need to provide the sevDesk API Token. 

Get your sevDesk API Token
1. Login to your sevDesk account.

2. Open user settings and select the user you want to use for sync.

3. In the user setting page click Show and copy API Token to clipboard.

Establish connection
1. Login to your Salesforce org.

2. Open sevDesk Application.

3. Select sevDesk setup tab, enter API Token and click Establish connection