Open your email signature in your device's browser app.
Tap and hold on some text in your email signature such as the name or role, then drag the selection handles to the bottom right and top left of the email signature and tap Copy.
Open your Outlook app.
Tap your account icon at the top left, then tap Settings at the bottom left of the menu and tap Signature.
Delete any text in your signature field, then tap and hold on the blank space and tap Paste.
Your email signature will be pasted, BUT, please note that table and cell structure will display here which is normal. These outlines will NOT show when you compose an email.
Close out of your settings and compose a new email. Your email signature will automatically appear when writing an email.