  The mutual competition and synergy of magnetism and superconductivity provide
us with a very valuable opportunity to access topological superconductivity and
Majorana Fermions. Here, we devise a heterostructure consisting of an $s$-wave
superconductor, a 2D topological insulator and an altermagnet, which is
classified as the third magnet and featured by zero magnetization but spin
polarization in both real and reciprocal spaces. We find that the altermagnet
can induce mass terms at the edges that compete with electron pairing, and mass
domains are formed at the corners of sample, resulting in zero-energy Majorana
corner modes (MCMs). The presence or absence of MCMs can be engineered by only
changing the direction of the N\'{e}el vector. Moreover, uniaxial strain can
effectively manipulate the patterns of the MCMs, such as moving and
interchanging MCMs. Experimental realization, remarkable advantages of our
proposal and possible braiding are discussed.
