Hi Boyte, William,
I assume that your assigned field is not a multi-user so you can use this json code to achieve your requirement
{
"$schema": "https://developer.microsoft.com/json-schemas/sp/v2/row-formatting.schema.json",
"groupProps": {
"headerFormatter": {
"elmType": "div",
"style": {
"padding-left": "12px",
"font-size": "16px",
"font-weight": "400",
"cursor": "pointer",
"outline": "0px",
"white-space": "nowrap",
"text-overflow": "ellipsis"
},
"children": [
{
"elmType": "div",
"children": [
{
"elmType": "span",
"style": {
"padding": "5px 5px 5px 5px"
},
"txtContent": "@group.fieldData.title"
}
]
}
]
}
}
}
Best regards,
IM