Some Bluetooth loudspeakers (and most Bluetooth headsets) must be in pairing mode when connecting to the phone for the first time.
Press and hold the power button on the Bluetooth speaker until an indicator light on the speaker blinks fast, then search for the speaker in the Bluetooth settings on the phone.
Please refer to the user manual for the loudspeaker or headset in case the pairing procedure is different for the specific accessory.
Some Bluetooth audio devices may need to first be unpaired from a previous phone. Please refer to the user manual (or try press and hold any +/- or up/down buttons on the loudspeaker until an indicator light blink or change colour, typically).
Does this help?