iMAC boot disaster need help!!!!!

hi

I know i messed up i dont to be told what i have done.

iMAC osx installed ---> on boot held opt key to get imac boot options booted off ubuntu 18.04 lts uefi -----> live cd ---> gpart deleted osx uefi partition ---> deleted osx recovery partition ---->

--> apple wireless mouse and kb did not work had to plug in usb keyboard and mouse to go to bluetooth settings and add them ----> now they work in UBUNTU ----> ubuntu install partition uefi boot partition / grub partition / swap and root (/)... installed ubuntu all working fine...

but now apple keyboard opt does not obviously bring boot options anymore, no grub appears to run recovery mode (not sure if there is a boot from cd/dvd option anyway)

i thought that opt cmd and o and f, brought up imac firmware where you could change boot options but nothing.

ubuntu is not playing well with my imac. problem is i cant boot off anything other than ubuntu and it that does wrong then nothing will boot.

i need to some how get ubuntu to offer a boot off external media ie my mac osx dvd then i could reinstall osx and get the thing working probably will dual boot.

but how do i fix this mess.

many many thx to anyone who could help.