How to export PGP key (in clear text?)?

How to export PGP key (in clear text?)?

I created a set of PGP keys in Kleopatra using GPG4Win. I want to use my
private and public keys to encrypt and decrypt emails with this Chrome
extension:
https://chrome.google.com/webstore/detail/mailvelope/kajibbejlbohfaggdiogboambcijhkke
I imported the public key fine, but it seems that the extension also needs
the private key. I am wondering how to export the private key (in plain
text I guess) so that I can use it in the extension. I can't believe I
have been unable to find a solution for this on my own, so any help is
deeply appreciated. Thank you.