My understanding is if a convention there would be another vote at the next election to send delegates too. From seacoast online paper

So, what happens if voters decide they want a constitutional convention this time around? In that case, voters would then be tasked with choosing delegates to the convention at the next election, similar to the process for choosing state representatives. Then, if three-fifths of those delegates agree on changes to the state constitution, the final changes would be put before voters at the next biennial election.

Considering the effort it takes to hold a constitutional convention, you may be wondering why anyone would want to. There are a variety of proposed constitutional amendments that have gained traction in recent years, including a constitutional ban on income/sales taxes, changes to legislator compensation (currently $100 a year plus mileage), a constitutional right to an abortion, and more.