After click Add button, you can specify Account Access, Contact Access, Opportunity Access, Case Access, and Team Role. If your default sharing in OWD is Private for that objects, you will see Private, Read Only, and Read/Write option in the picklist. You can add up to 5 users every time add team member manually.
But, if you need to add users into hundreds of account team member, manual process is not fun.
So, here is the solution. Use Data Loader to mass create AccountTeamMember records and AccountShare records.
1. Account Team Member
The API name is AccountTeamMember, you need to populate following fields when mass insert into AccountTeamMember:
Note: creating this record will not allow user added into AccountTeamMember to access Contact, Opportunity, Case if the sharing setting is Private. TeamMemberRole value can be different with values defined in Team Role.
Purpose: it will show user added into Account Team related list.
2. Account Share
The API name is AccountShare, you need to populate following fields when mass insert into AccountShare:
- CaseAccessLevel [optional]
- ContactAccessLevel [optional]
- OpportunityAccessLevel [optional]
You can set Private, Read Only, and Read/Write in above fields optional if default sharing in OWD is set to Private.
Note: user added into Account Share will be able to access Case, Contact and Opportunity records with Read Only or Read/Write permission, even it is not shown in Account Team related list.
Here is more information on mass create manual sharing rules with the Data Loader, click here.