//Hi jay you can refer the below code for updating multiple value in multiple people and group field
var getId=get_id();
data: { "__metadata": { "type": "SP.Data.ListNameListItem" }, "AssignedToId": { "results": [getId,getId] } };
 
//And for single value you can use below
data: { "__metadata": { "type": "SP.Data.ListNameListItem" }, "AssignedToId": { "results": [getId] } };

You can refer to the below code for updating multiple value in multiple people and group field:

var getId=get_id();
data: { "__metadata": { "type": "SP.Data.ListNameListItem" }, "AssignedToId": { "results": [getId,getId] } };

And for single value you can use:

data: { "__metadata": { "type": "SP.Data.ListNameListItem" }, "AssignedToId": { "results": [getId] } };