You need to use a tin tool in order to stick the chip , something like
this.
What happens is that after you heat the solder on the chip to remove it and since it has already been heated the first time it was installed the solder is no longer good enough to make 100% contact so you need to re-do the tin/solder process,you have to use a liquid solder for this.
Place a bit of flux and drop that chip, make sure you position it perfectly and the flux will make it easier , then use something like a pick to push the chip down while heating it from the top.