How to use a the same generated keypair on enigmail/thunderbird and iOS Mail

[E.Keen]

Dear community,

I am very passionate about cyber security and working against mass
surveillance. I therefore try to stay informed about security
measurements and encryption.

Nevertheless, I do have a problem which I cannot solve by myself.

I generated a keypair using enigmail on thunderbird for this email address.
Now, I'd like to use the same address with the same encryption keys on
an iOS device.
However, I don't know how to transfer the private key securely without
anyone else being able to obtain it.
Someone informed me that there might be a possibility to type in the
private key manually.

I 'd appreciate any help or further information you might give me.

Thank you very much.

Kind Regards,

E.Keen