the first step you need go to your Cpanel >> file manager>> go to your Orderform template to find products.tpl
Click on it and edit it search for {$product.pricing.minprice.cycleText} replace it with the code bellow.
{if $product.pricing.rawpricing.annually neq -1}<span>{$currency.prefix}{($product.pricing.rawpricing.annually/12)|string_format:"%.2f"}{$currency.suffix}</span>/mo{else}{$product.pricing.minprice.cycleText}{/if}
this code will divide your yearly price into 12 months, so if you would like to change it to 2 years you need to change the number of months so 2 years 24 months and 3 years 36 months
here the code only you need to copy and paste.
2 years code :
{if $product.pricing.rawpricing.biennially neq -1}<span>{$currency.prefix}{($product.pricing.rawpricing.biennially/24)|string_format:"%.2f"}{$currency.suffix}</span>/mo{else}{$product.pricing.minprice.cycleText}{/if}
3 years code :
{if $product.pricing.rawpricing.triennially neq -1}<span>{$currency.prefix}{($product.pricing.rawpricing.triennially/24)|string_format:"%.2f"}{$currency.suffix}</span>/mo{else}{$product.pricing.minprice.cycleText}{/if}
so here second step to assign your selection
go to your Cpanel >> file manager>> go to your Orderform template to find configureproduct.tpl
Click on it and edit it and add this code by the beginning of the page and change the bill-cycle name to your selection.
{assign billingcycle "triennially"}