Based on the context, this is what you may try:
1. Manual merging in the editor:
You can create a new animation and manually copy the animation keys from your existing animations into it. However, depending on what properties you keyed in each animation, you may encounter conflicts that could make the combined animation look different from playing them back on separate tracks.
2. Using Unity with Timeline Extension:
If you're working with Unity, you can use the Timeline Extension to export sequences that combine multiple animations without writing code. There's a step-by-step tutorial video available to guide you through this process.
3. Preview the combination:
While it won't export as a merged animation, you can use the Preview view to play multiple animations on different tracks simultaneously to see how they work together before attempting a manual merge.
The manual approach may be tedious, but it's currently the only way to achieve a true merged animation within the editor itself.
