Randomly LENGTHENING an antenna would probably do more harm than good, if the antenna was competently designed, originally.
I believe that the suggestion was to try using an EXTERNAL antenna, not to lengthen the existing antenna.
You would also need a properly-matched controlled-impedance transmission line (e.g. a coaxial cable) in order to get good performance from an external antenna. And the external antenna would need to be optimized for the RF's frequency and the transmission line's impedance.
I believe that the suggestion was to try using an EXTERNAL antenna, not to lengthen the existing antenna.
You would also need a properly-matched controlled-impedance transmission line (e.g. a coaxial cable) in order to get good performance from an external antenna. And the external antenna would need to be optimized for the RF's frequency and the transmission line's impedance.