To set up an IVA (Individual Voluntary Agreement) you will need to apply to a company that deals with IVA's or direct to an Insolvency Practitioner (IP). Once your initial application has been approve your IP will inform your creditors on your behalf that you are applying for an IVA. You will not normally need to contact your creditors directly.
Once an interim order has been granted your creditors should not contact you directly, instead all communications should go via your IP. An IVA proposal will be presented to your creditors on your behalf at the creditors meeting, where the vote will take place to determine whether the IVA will go ahead.
Once the IVA period has started all dealing between you and your creditors should go through the Insolvency Practitioner.