How to preset a dropdown value

DefaultSelectedItems

Table(
        {
           Value: "your value"
        }
)

———————————————

Totorial found at:
https://powerusers.microsoft.com/t5/Building-Power-Apps/Update-Choice-field-with-a-button-OnSelect/m-p/302503

Set OnVisible = Set(ChoiceVar, Blank())

Set the OnSelect property of the “Button” to following:

Set(ChoiceVar, {Value: "Closed"})

Set the DefaultSelectedItems property of the ComboBox within the Choice field Data card to following:

[code]If(
!IsBlank(ChoiceVar),
ChoiceVar,
Parent.Default
) [/code]

If(frmEdit.Mode = FormMode.New, LookUp( Choices('dbconn'.field), Value = "something"), Parent.Default)

Preset a Lookup choice field:

//Choices([@'DS'].'MSB Org')
If(
    frmEdit.Mode = FormMode.New,
    {
        Value: "Something",
        '@odata.type': "#Microsoft.Azure.Connectors.SharePoint.SPListExpandedReference",
        Id: 2
    },
    Parent.Default
)