The Swantide App currently supports creating certain types of custom fields, including:
Picklist
Text
URL
Number
Email
Date
Phone
For any other field types (e.g. checkbox fields, formulas), you will need to create those in Salesforce. This guide walks through how to best do this.
Step 1: Navigate to the Object you will be creating fields
Click on the gear icon in the upper right hand of Salesforce. Click on Object Manager, and then search for the object in question. On the left hand side, select 'Fields and Relationships'
Step 2: Create fields
Click 'New' in the upper right hand corner. Follow the steps in the wizard to create your field. Make sure that the field is visible to all profile types, and that it is added to all page layouts in the final step of the process.