What is the correct wording to be used for announcement or invitation for a person who is preaching their trial sermon?

It may vary from one denomination to another. However, a common Wording in written form for the public might be:

The congregation of [church name] invites you to attend our worship service where the Reverend [full name] from [location] will be preaching his trial sermon. [You can include the Title of the sermon here, if you want.] The service will be at [time] on [date] at [address of church]. Fellowship will be held after the service. All are welcome.

At the service, introduce the Reverend with some short biographical information, such as: Reverend [last name] recently graduated from [theological seminary or school]. She/he joins us today to talk on the subject [use the same title the Reverend is using for his sermon]. Please welcome Reverend [last name]. [Or, now I will turn over the microphone to Reverend (last name).]

Don't forget to send a Thank-you card afterward.