Custom Form Enhancement: Ability to pre-populate drop down field with "Start Typing" or another phrase to indicate that scrolling is not only search option

Would like to enhance the UI of a large dropdown list so users know that it's searchable.

For example: pre-populate the beginning drop down field with the words "start typing" (or another indicator) to prompt users to begin typing their choice so they know it's possible to search via text and their only option isn't to to sort through 100s of entries using drop down function only.