If you are claiming (amongst other things) loss of earnings, you are expected to mitigate your losses. This means that you are expected to take reasonable steps to find alternative employment while you are waiting for your claim to be heard.
The tribunal will decide whether you have taken reasonable steps to do this, and your employer may argue that you have not done so. However, your employer will have to prove this, for example by providing evidence of jobs you could have applied for or carried out. Your employer will have to show that you acted unreasonably in not taking reasonable steps to secure alternative employment.
If a tribunal finds an employee has unreasonably failed to mitigate their loss, compensation may be reduced by an amount that the tribunal considers appropriate.