Expiring contracts automatically appear in 'My tasks' under the right manager (the manager that is task owner of the 'Renew or end contract' task of that team) list well before the end date.
From the task, you can offer a renewal directly (either with end date or indefinite) or end the contract. When an employee is on contract number 3 in the chain of contracts you have to offer them an indefinite contract. This is Dutch law.
Converting to permanent: close the current contract on the desired end date and create a new contract starting the day after. Soigné recognises the continuous period and treats it as ongoing employment, anciënniteit (seniority) and accrued rights stay intact. Set end date of the contract to 'indefinite'.
Want to give someone an indefinite contract before their current contract ends? Chat with Soigné Support to arrange that.
Changing terms mid-contract (hours, salary)? Create an addendum from an employee their profile under Employment → ⋮ (more options) → Create addendum. The original contract stays; the addendum sits below it and is signed separately. The part that will be changed on the contract will show as purple in the pop-up to create the addendum.
Be aware that you are not able to create an addendum when someone currently has a contract offered to them that needs to be signed first.