Conversion of equity shares into non participating preferenc

Dear Expert,

We have a Private Company in which one of the major Shareholder wants to return his shares to the Company (Buy Back) , but Company don't have funds to buy back . Therefore Shareholder wants to his equity shares into the Non participating preference shares @ 6% p.a. for the 20 years.

Kindly suggest the best possible methods for conversion of equity shares into the Non Participating Preference Shares for the 20 years @ 6% and do the needful.

Thanking You,

Regards,

Rachana Daga.