What is the slave address of the STM32 NUCLEO-F401RE?
You should have searched the Reference Manual of the controller. But as said the MCU's I2C address can be set from software through dedicated registers.

These are called Own Address Register 1 and 2. For the most simple 7-bit addressing mode you have to clear the ADDMODE bit and set any kind of address you want using ADD[7:1] bits.

Here are the relevant register descriptions but I suggest to read through the entire I2C chapter of the linked document.