Is there an a method to fit a wave created from two wave?
As a precautionary statement, the FFT will give you coefficients of the frequency components closest to the integer multiples of $1/T$ in Hz where $T$ is the length of the sequence in seconds being used for the FFT. If the components are not on these integer boundaries, then you will get several results (called spectral leakage) where the actual components (if information is known such as in the OP’s case of having just two tones) can be estimated as being in between two large adjacent results.
Further when combining the waveform you must pay attention to the phase as well as amplitude of the result in order for it to match the time domain waveform shown. The FFT will provide both a scaled magnitude and phase. The FFT results are the coefficients for complex frequencies (of the form $e^{j\omega t}$ but if it is known that the waveform is real then you can use the first half of the FFT as representing the coefficients of real frequencies in the form of $\cos(\omega t)$, scaled by $N/2$ where $N$ is the number of samples in the sequence used for the FFT.