When I enter a record on form..It must be empty and unless I select it from the list.
You have to add an empty value in your ComboBox/List and make sure that empty value should be at top. If Combo Box is coming from BaseEnum, keep value 0/least for empty element.
That is default behavior, a value is selected by default as must.
In the second form... When I select the Plant in that record.. It must navigate to Plant form. If i select a Other record on that form..It must navigate to the Other form.
Use if condition and call form by code
If(Plant|)
{
Navigate/ open Plant Form
}
else
{
call other form
}
you may also think to use Switch Case