You can't, if you've followed the instructions correctly.

On Windows, click Wallet -> Information. The window which pops up will have a box titled "Master Public Key" at the bottom. Within will be a master public key starting with "zpub" (or maybe "xpub" or "ypub", depending on the specifics of your wallet). Use that key (and only that key) to create your watch only wallet on Android.

If you've done this, you cannot spend from your Android wallet. It will let you enter an address, enter an amount, set a fee, and actually create a transaction, but it will be unable to sign or broadcast that transaction. Instead, it will tell you to present that transaction to the "signing device". If you don't do that, then the transaction cannot be signed and your coins cannot be spent.