The reality is that you can choose between cancel the entire ticket/full refund (not partial refund for the LIS-MAN segment only) or rebooking to other TAP flights (the entirety/all flights of the ticket).

From experience there is zero chance that TAP will accept to rebook to other carriers or even Star Alliance Partners this far out. So you can rebook to TAP flights on a different date with a better/shorter connection time at LIS; I can not rule out that TAP may agree to rebook to LHR if you prefer this. If this doesn't work, you can request to cancel and get a full refund and book a ticket elsewhere.