Terraform Custom Provider Read Values

Question

I am making custom terraform provider, there is a optional input for the labels, but what I find the challenge is that strings use .ValueString() to retrieve the values from main.tf, uncertain what to use for types.MapType.

Here is the code:

type ResourceModel struct {
    InstanceName   types.String  `tfsdk:"instance_name"`
    Id             types.String  `tfsdk:"id"`
    Labels         types.MapType `tfsdk:"labels"`
}

func (r *vmResource) Schema(_ context.Context, _ resource.SchemaRequest, resp *resource.SchemaResponse) {
    resp.Schema = schema.Schema{
        Attributes: map[string]schema.Attribute{
            "instance_name": schema.StringAttribute{
                Required: true,
            },
            "id": schema.StringAttribute{
                Required: true,
            },
            "labels":schema.MapAttribute{
                Optional: true,
            },
        },
    }
}

    var plan ResourceModel
    diags := req.Plan.Get(ctx, &plan)

    if resp.Diagnostics.HasError() {
        return
    }

    request := VmCreate{
        InstanceName:   plan.InstanceName.ValueString(),
        Id:             plan.Id.ValueString(),
        Labels:         plan.Labels.????
    }

Tried to find the solution but all i tried failed.