It's easy to update fields for multiple records at once - here's how:
Go to the Data Explorer, and ensure your desired model is selected
Use the checkboxes to select all of the records (e.g. Companies) where you would like to bulk edit a field. Typically you would create a filter and then select all of the results from the filter. You can refer to the Data Explorer article for information on how to apply a filter here
Click the image to view it enlarged
Once you have selected the records, click on "Set Field"
Choose which field to edit (from the dropdown menu), and then select the value you'd like to set for the field
📌 Important to note: bulk updating overwrites existing field values, so be careful, especially when updating fields which may have multiple values, such as a multipicklist, since existing entries will be replaced.